2. Prefertilization events
Sexual reproduction
-occurs when female & male gametes unite at fertilization
A. Gametes
-PGC from wall of the yolk sac at week 4 migrate into future gonad region
- are produced by gametogenesis (oogenesis in the female and spermatogenesis in the male)

3. Chromosomes Single & duplicate Normal somatic cells & PGC;
-46 single and 2N amount of DNA or 23 homologous pairs or diploid
- pairs 1 to 22 are autosomal (non-sex) pairs
-pair 23 consists of the sex chromosomes (XX for a female XY for a male)

4. Gamates;
-contain 23 single chromosomes or haploid (22 autosomes and 1 sex chromosome) and 1N amount of DNA
-female gametes contain only the X sex chromosome
-male gametes contain either the X or Y sex chromosome: male gamete determines the genetic sex

6. Meiosis1
-DNA replication
-synapsis
-crossover
-alignment
-disjunction
-cell division
Meiosis2

8. Human birth defects Enviromental or genetic factors
Agents that cause congenital malformation is teratogens
About 3% liveborn infants have defects at birth this statistic doubles by the end of the first postnatal year
Approximately 20% of infant deaths in the USA result from birth defect

9. Numerical chromosomal abnormalities
If one additional chromosome is present, the condition is called trisomy
If one chromosome is absent, the condition is called monosomy
Trisomy and monosomy are most often caused by meiotic nondisjunction of chromosom

10. Autosomal abnormalities
Trisomy 21 (Down syndrome)
-Mother under 25 is 1:2000
-mother 35 is 1:300
-mother 40 is 1:100
-mother over 45 is 1:25
-May affect all parts of the brain; mental retardation, microcephaly, microphthalmia, colobomata, cataracts, glaucoma
-epicanthic folds, simian crease, congenital heart defects, umbilical hernia & duodenal atresia
Alzheimer neurofibrillary tangeles and plaques found in the brains of persons over 35 years

11. Trisomy 18 (Edwards` syndrome)
Incidence is 1:5000
Infants usually die soon after birth (2 months)
Mental retardation, congenital heart defects, prominent occiput, low-set ears, micrognathia, flexed digits

12. Trisomy 13 (Patau syndrome)
Is much less common than 21
Incidence is 1:20000
Infants usually die soon after birth (3 months)
Mental retardation, microphthalmia, congenital heart defects, deafness, colobomata, cleft lip and cleft palate

13. Sex chromosome abnormalities klinefelters syndrome (47 XXY)
Is found only male with an incidence 1:500 male births
Male hypogonadism, sterility & gynecomastia
Some persons with this syndrome have 48 chromosomes (44 autosomes & 4 sex chromosome 48 XXXY

14. Turner syndrome (45 XO)
Is found only in females, with an incidence of 1:5000 live female births
Female hypogonadism (gonadal dysgenesis)
Sex chromatin negative
Infantile genitalia, hypoplastic ovaries, congenital heart defect, webbed neck, lymphedema of the extermities

15. Triple X syndrome Has an incidence of 1:960 births
Presence of two sex chromatine bodies (Barr bodies)
Usually fertile & 20% are mildly mentally retarded
Santhi Soundarajan

16. Structural abnormalities cri-du-chat syndrome
Results from deletion of the short arm of chromosome 5
Has an incidence of 1: births
Mental retardation, microcephaly, congenital heart defects, and a cat like cry

17. Contiguous gene syndrome
Angelman syndrome;
-is associated with deletion of band q12 on chromosom15 (found in the mother)
-mental retardation, sezures, and dystaxia

18. Prader-willi syndrome
- is associated with deletion of band q12 on chromosom15 (found in the father)
- mental retardation, hyperphagia, and hypogonadism

19. Gene mutation
Genes exits as pairs, or alleles (exception of the X & Y chromosomes in the male).
If a mutant gene gene produces an abnormality in a single dose, despite the presence of a normal allele, it is a dominant mutation.
If both alleles must be abnormal (double dose) or if the mutation is X-linked in the male, it is a recessive mutation.

20. Diagnostic techniques for identifying genetic abnormalitis
Cytogenetic analysis
High resolution metaphase banding techniques
Fluorescence in situ hybridization (FISH)
Spectoral karyotype analysis (SKY)

21. Oogenesis
PGC; arrived in gonad at week 4, differentiate into oogonia , then mitotic division , differentiate into primary oocytes
All primary oocytes are formed by fifth month of fetal life; no oogonia are present at birth
primary oocytes remain dormant in prophase of meiosis1 from fifth month of fetal life at least until puberty (about age 12), after puberty 15 to 20 primary oocyte will begin maturation with each ovarian cycle, with usually only one reaching full maturity in each cycle.
After puberty, a primary oocyte completes meiosis1 to form two daughter cells: the secondary oocyte and the first polar body
The secondary oocyte enters meiosis2 when the chromosomes align at the metaphase plate, ovulation occures. After this point, oogenesis is complated outside the ovary, in the uterine tube where fertilization usually occures
The secondary oocyte remains arrested in metaphase of meiosis2 until fertilization occurs
At fertilization, the secondary oocyte will complete meiosis2 to form a mature oocyte and a second polar body

22. Approximate number of oocytees;
-primary oocytes; 7 million at 5 months
2 million at birth
at pubert
-secondary oocytes; 12 ovulate per year
up to 480 reproductive
-reduced; birth control pills, women pregnant

25. Oogenesis & Spermatogenesis

26. PGC; arrive in gonad at week 4, remain dormant until puberty
At puberty; differentiate into spermatogonia
Spermatogenesis
spermiogenesis